1. Field of the Invention
The present invention relates to a vent check valve assembly and more particularly to a device which is mounted on the vent outlet of a pump or sampler to prevent the overflow of the pumped or sampled fluid. One such use of the present invention is in the field of odorant injection systems wherein an odorant is injected into a natural gas pipeline and the vent check valve assembly is used to prevent the loss of odorant if the odorant pump fails.
2. Description of Related Art
A preferred use of the present invention is in the area of injecting liquid chemicals into a gas. For example, natural gas is generally odorless until an odorant such as ethyl mercaptan (ethanethiol) is injected into the gas as it flows through a pipeline. Currently available odorant injection systems include a storage container for the odorant, a chemical pump and an injection nozzle. These systems also include various level and flow sight glasses as well as filters and check valves between the storage container, pump and the injection nozzle.
The odorant injection systems are typically located at remote metering stations or gas distribution stations or substations so that gas leaks may be detected in cities or other populated areas. Therefore, the natural gas in larger pipelines is usually odorless while residential or commercial gas lines include an odorant dispersed in the gas. Because of the combustibility of the odorant and the gas, the odorant injection system is oftentimes exposed to the elements or housed in a small building at a distribution center which may or may not be monitored.
A number of patents have been granted for various odorant injection systems. For example, U.S. Pat. No. 2,175,526 was granted to Hutchinson, et al. In the Hutchinson, et al. patent, a portion of the gas flowing through the pipeline is diverted into the odorant injection system to be mixed with the odorant and then subsequently returned to the pipeline. U.S. Pat. No. 2,166,370 granted to Putnam, et al. discloses another odorant injection system. The Putnam, et al. patent discloses the use of a pressure sensor in the pipeline which is connected to a lever which controls the flow of the odorant into the pipeline. U.S. Pat. Nos. 3,112,189; 4,007,755; 4,025,315 and 4,611,294 disclose further systems and methods for injecting an odorant into a pipeline.
The chemical pumps used in many currently available odorant injection systems typically include odorant inlet and outlet openings as well as a vent opening. The vent opening is located below the piston of the pump and in flow communication with the piston chamber of the pump to prevent the buildup of a back pressure in the pump. In the current pumps, this vent opening is open to the atmosphere. Because these pumps are not infallible and because maintenance on these pumps may not be performed on a regular basis, the seals on the pumps may occasionally fail. If this occurs, the pump will continue to operate and the odorant will be pumped out of the vent outlet rather than through the odorant outlet. This occurs because the odorant will normally take the path of least resistance through the vent outlet rather than past a poppet valve which is positioned adjacent to the odorant outlet. If the odorant is spilled, the company will be required to clean up the spill and may also face various fines from regulatory agencies such as the Environmental Protection Agency. Additionally, with the unprotected vent outlet, it is possible for various insects such as bees or wasps to plug or otherwise obstruct or introduce contaminants into the vent outlet, thereby decreasing the efficiency and expected life of the pump by increasing the pressure necessary to move the piston in the piston chamber of the pump.
The present invention overcomes the disadvantages of the currently available odorant injection systems by providing a vent check valve which attaches to and covers the vent outlet of the chemical pump while allowing the flow of air therethrough during normal operation of the chemical pump. Additionally, the present invention prevents accidental flow of odorant from the odorant injection system in the event that the seals in the chemical pump fail.